Buy some JB Weld. It's a two-part epoxy contained in two squeeze tubes which are combined together and mixed when you need to make a repair. This stuff will set up as hard as metal. It can be drilled, sanded, painted, etc. Big Box stores or auto parts retailers should all have it on the shelf.

You can also fiberglass (with epoxy resin) those holes...Paul repaired our rusted-through lawnmower deck with fiberglass (in his early, trial days of fiberglassing last winter...) -- it worked great! (Epoxy resin sticks to everything...including your sanity!)

JB Weld is also awesome. We repaired a range oven handle (totally broken off) with it once. Twelve years later it was still perfectly attached. We sold the range with the house when we moved.

If you want the similar shiny metal look of the aluminum, you could solder the holes closet.
Dave & Paula

Where can I find aluminum solder? I need to buy some of that for my shop, All the solder I've ever used is made of lead and will not stick to aluminum. You could weld them closed but would have to remove the window frame to do that without burning down your trailer.

Another option is Bondo autobody filler. It's cheap, has a long shelf life, sets quickly and is easy to finish. I use it for lots of off label things like rebuilding brick molding and wooden boat repair.

It never ceases to amaze me why some people feel compelled to complicate what should be simple fixes by offering up their opinions and suggestions on all manner of exotic "how-tos" to fix things, which if you really look at them, are somewhat "out there". The OP just wanted a quick fix without a lot of hassles. Do you really think that she would want to perform such tasks as fiber-glassing, soldering, welding, grinding, etc, just to fix a few small holes in a window frame? Come on folks, lets try to be a bit more focused on the simple methods rather than trying to overly complicate correcting problems. Rant over.

It never ceases to amaze me why some people feel compelled to complicate what should be simple fixes by offering up their opinions and suggestions on all manner of exotic "how-tos" to fix things, which if you really look at them, are somewhat "out there". The OP just wanted a quick fix without a lot of hassles. Do you really think that she would want to perform such tasks as fiber-glassing, soldering, welding, grinding, etc, just to fix a few small holes in a window frame? Come on folks, lets try to be a bit more focused on the simple methods rather than trying to overly complicate correcting problems. Rant over.

Some folks are perfectly happy with just a solution no matter what it looks like. Others want a solution that fixes the problem where it turns the fix invisible. It's about choice and that's what we're here for. The OP wasn't looking for a "quick fix" as you mentioned, but "best for filling in screw holes." I consider it different strokes for different folks Greg.

I'm going to try the JB weld first. Since I have many screw holes to fill, if I don't like the results, I'll try something else.

I like hearing about all the options. It might help someone in the future as searching these forums is how I've found out about most of my repair options for my Boler. I'm slowly repairing her by my lonesome (my father is too ill now to help much) and have learned that, despite my enthusiasm, I'm not the most imaginative when it comes to repairs! If it requires more than basic skills, honestly, I'm probably not going to try it. Soldering, not my forte; grinding with a Dremel or filling in with a malleable product, I can do!